Reduce consing during SUBTYPEP on classes.

sb-pcl::class-has-a-forward-referenced-superclass-p, used in the
implementation of subtypep on classes, conses because SOME can't
perform the required inlining when used on the sequences of unknown
type. (See lp#1070635)
Make sure quantifiers don't cons

Quantifiers like SOME and EVERY are implemented in terms of (MAP NIL)
of a wrapper function with early RETURN. If type information does not
enable MAP to be open coded, declarations are necessary to avoid
consing up a closure and a value cell for the return.

DX functions really shouldn't cause value cells for return blocks.

Also, revert d0f65b07a30adc989e36a82ddc0ed54d135d638e which is
now mostly redundant.